JP2007297989A - Cylinder injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylinder injection type spark ignition internal combustion engine capable of securely strengthening a tumble flow of which strength is changed in accordance with kinetic energy of intake air supplied to inside of a cylinder by injected fuel and of suppressing fuel adherence to a cylinder bore. <P>SOLUTION: A fuel injection valve 1 arranged approximately in the center of the upper part of the cylinder and an ignition plug 2 arranged in the upper part of the cylinder are provided. To strengthen the tumble flow T whirling around inside of the cylinder by descending along an exhaust valve side of the cylinder bore and ascending along an intake valve side of the cylinder bore, fuel F is injected toward the exhaust valve side of the cylinder bore by the fuel injection valve 1 at a last stage of an intake stroke. When the kinetic energy of intake air forming the tumble flow T at the time of inflow into the cylinder is small, an injection rate of the fuel injected from the fuel injection valve 1 to strengthen the tumble flow T is reduced, compared to the case where the kinetic energy is large. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a direct injection spark ignition internal combustion engine.

  In homogeneous combustion in which a homogeneous mixture is formed in the cylinder and this homogeneous mixture is ignited and combusted at the ignition timing at the end of the compression stroke, a tumble flow is formed in the cylinder by the intake air supplied into the cylinder, and this tumble flow is By maintaining the ignition timing at the end of the compression stroke until the ignition timing causes turbulence in the cylinder due to the tumble flow, and this turbulence can increase the combustion speed of the homogeneous mixture, good homogeneous combustion can be realized. it can.

  In order to maintain the tumble flow until the ignition timing at the end of the compression stroke, an intake flow control valve is arranged in the intake port, and by this intake flow control valve, intake air is supplied into the cylinder along the upper wall of the intake port. An in-cylinder injection spark ignition internal combustion engine that forms a strong tumble flow in a cylinder has been proposed (see, for example, Patent Document 1).

JP 2005-180247 A JP2004-190548 JP 2002-227651 A

  In the above-described in-cylinder spark ignition internal combustion engine, when intake air is supplied into the cylinder along the upper wall of the intake port by the intake flow control valve, the intake port is throttled by the intake flow control valve. As a result, when the required intake air amount is relatively small, a strong tumble flow can be formed in the cylinder without any problem. However, when the required intake air amount is relatively large, the intake port is controlled by the intake air flow control valve. Since a shortage of intake may occur if the throttle valve is throttled, a strong tumble flow cannot be formed in the cylinder by the intake flow control valve.

  As a result, without arranging such an intake flow control valve, a tumble flow rotating in the cylinder so as to descend along the exhaust valve side of the cylinder bore and ascend along the intake valve side of the cylinder bore, It is conceivable that the fuel injection valve arranged at the substantially upper center of the cylinder at the end stage is strengthened by utilizing the penetration force of the fuel injected toward the exhaust valve side of the cylinder bore.

  However, since the kinetic energy of the intake air supplied into the cylinder changes depending on the engine operating state, and the strength of the tumble flow generated in the cylinder changes according to this kinetic energy, the penetration force of the injected fuel is increased. When set, when the strength of the tumble flow generated in the cylinder becomes relatively weak, the injected fuel may penetrate the tumble flow and adhere to the cylinder bore, thereby diluting the engine oil. If the penetration force of the injected fuel is set to be weak, the tumble flow cannot be increased when the strength of the tumble flow generated in the cylinder becomes relatively strong.

  Accordingly, an object of the present invention is to ensure that the tumble flow whose strength changes in accordance with the kinetic energy of the intake air supplied into the cylinder can be reliably increased by the injected fuel, and to suppress the fuel adhesion to the cylinder bore. It is an object of the present invention to provide an in-cylinder injection spark ignition internal combustion engine.

  According to a first aspect of the present invention, there is provided an in-cylinder injection spark ignition internal combustion engine comprising a fuel injection valve disposed substantially at the center of a cylinder upper portion and an ignition plug disposed at an upper portion of the cylinder, the exhaust valve side of the cylinder bore The fuel injection valve injects fuel toward the exhaust valve side of the cylinder bore at the end of the intake stroke in order to strengthen the tumble flow that turns in the cylinder so as to descend along the intake valve side and rise along the intake valve side of the cylinder bore. When the kinetic energy when the intake air generating the tumble flow flows into the cylinder is small, the fuel injected from the fuel injection valve to intensify the tumble flow compared to when the kinetic energy is large. The injection rate is lowered.

  The direct injection spark ignition internal combustion engine according to claim 2 according to the present invention is the direct injection spark ignition internal combustion engine according to claim 1, wherein the smaller the kinetic energy of the intake air that generates the tumble flow, The injection rate of the fuel injected from the fuel injection valve is lowered.

  According to a third aspect of the present invention, there is provided an in-cylinder injection spark ignition internal combustion engine according to the second aspect of the present invention, wherein the fuel injection valve has a high lift amount and a low lift amount. The fuel injection with the maximum injection rate can be realized by opening the valve body for the high lift amount, and the minimum injection rate can be controlled by opening the valve body for the low lift amount. Fuel injection is realized, and the injection rate between the maximum injection rate and the minimum injection rate is realized by continuously opening the valve body at one or the other of the high lift amount and the low lift amount. It is characterized by doing.

  According to the in-cylinder injection spark ignition internal combustion engine of the first aspect of the present invention, in order to strengthen the tumble flow, fuel is injected toward the exhaust valve side of the cylinder bore by the fuel injection valve at the end of the intake stroke. When the kinetic energy when flowing into the cylinder of the intake air that generates the flow is small, the injection rate of the fuel injected from the fuel injection valve is lowered to increase the tumble flow compared to when the kinetic energy is large It has become. As a result, when the kinetic energy of the intake air when flowing into the cylinder is small, the strength of the tumble flow becomes relatively weak, and at this time, the injection rate of the fuel injected from the fuel injection valve is lowered, so that the injection The penetration force of the fuel is weakened, and the injected fuel is prevented from penetrating through the tumble flow and adhering to the cylinder bore. Further, since the strength of the tumble flow is relatively weak, the tumble flow can be surely strengthened even by the injected fuel whose penetrating force is weakened. Also, when the kinetic energy when flowing into the intake cylinder is large, the strength of the tumble flow becomes relatively strong. At this time, the injected fuel with weak penetrating power cannot strengthen the tumble flow, Since the injection rate is increased, the penetration force of the injected fuel is increased, and the tumble flow can be reliably increased. In addition, since the strength of the tumble flow is relatively strong, even if the penetration force is increased, the injected fuel hardly penetrates the tumble flow, and adhesion of the injected fuel to the cylinder bore is suppressed.

  According to the in-cylinder injection spark ignition internal combustion engine according to claim 2 of the present invention, in the in-cylinder injection spark ignition internal combustion engine according to claim 1, the intake air that generates the tumble flow flows into the cylinder. The greater the kinetic energy at which the fuel is injected, the lower the injection rate of the fuel injected from the fuel injection valve. As a result, the penetrating force of the injected fuel becomes weaker as the strength of the tumble flow becomes weaker, and the penetrating force of the injected fuel becomes stronger as the strength of the tumble flow becomes stronger. In addition, it is possible to sufficiently suppress fuel adhesion to the cylinder bore.

  Further, according to the in-cylinder injection spark ignition internal combustion engine according to claim 3 of the present invention, in the in-cylinder injection spark ignition internal combustion engine according to claim 2, the fuel injection valve has a high lift amount. The fuel injection with the maximum injection rate is realized by opening the valve body with the high lift amount, and the fuel with the minimum injection rate is opened with the valve body opening with the low lift amount. Injection is realized, and the injection rate between the maximum injection rate and the minimum injection rate is realized by continuously opening the valve body at one and the other of the high lift amount and the low lift amount. . Thereby, the injection rate can be changed in multiple stages in accordance with the strength of the tumble flow also by the two-stage lift amount control of the valve body.

  FIG. 1 is a bottom view of a cylinder head showing an embodiment of a direct injection spark ignition internal combustion engine according to the present invention, and FIG. 2 is a schematic longitudinal sectional view of the direct injection spark ignition internal combustion engine of FIG. In these drawings, reference numeral 1 denotes a fuel injection valve that is disposed substantially at the center of the cylinder and injects fuel directly into the cylinder, and 2 is a spark plug that is disposed in the vicinity of the fuel injection valve 1. 3 is a piston, 4 is a pair of intake valves, and 5 is a pair of exhaust valves.

The in-cylinder injection spark ignition internal combustion engine forms a homogeneous air-fuel mixture that is leaner than the stoichiometric air-fuel ratio in a cylinder and performs homogeneous combustion in which the air-fuel mixture is ignited and burned by an ignition plug 2. The lean air-fuel ratio of this homogeneous combustion is set so that the amount of NO _x produced is relatively small (for example, 20). For example, when the engine speed is high and the load is high, homogeneous combustion at the stoichiometric air-fuel ratio or rich air-fuel ratio may be performed. Further, when the NO _X storing catalyst apparatus for storing the NO _X when the air-fuel ratio of the exhaust gas in the engine exhaust system is lean is located, to release the occluded NO _X from the NO _X storing catalyst apparatus reducing and purifying When performing, homogeneous combustion is performed with the combustion air-fuel ratio set to the set rich air-fuel ratio. In particular, in homogeneous combustion at a lean air-fuel ratio, a desired engine output cannot be obtained unless the combustion speed is increased by causing turbulence in the cylinder at the ignition timing. Thereby, a tumble flow T that descends the exhaust valve side of the cylinder bore and rises the intake valve side by intake air supplied into the cylinder in the intake stroke is formed in the cylinder, and this tumble flow T is used as the ignition timing at the end of the compression stroke. It is preferable that turbulence exists in the cylinder at the ignition timing.

  However, the tumble flow generally formed in the cylinder is not so strong unless the cylinder head is thickened and the shape of the intake port is devised, or the intake flow control valve is provided in the intake port. Even if the cavity 3a having a partial arc cross section for suppressing the attenuation of the tumble flow is formed on the top surface of the piston 3 as in the present embodiment, it is not possible until the ignition timing due to the attenuation during the compression stroke. It disappears easily, and turbulence cannot exist in the cylinder by the tumble flow at the ignition timing. Thereby, in the present embodiment, the tumble flow T formed in the cylinder in the intake stroke is utilized by the penetration force of the fuel F injected by the fuel injection valve 1 toward the exhaust valve side of the cylinder bore at the end of the intake stroke. And strengthen it. The strengthened tumble flow can be sustained well until the ignition timing at the end of the compression stroke, and the turbulence can exist in the cylinder.

  In the present embodiment, the fuel injection valve 1 has, for example, a slit-shaped injection hole and injects fuel into a substantially thin fan shape, and the center plane in the width direction of the fuel spray F is a tumble flow. It is made to substantially coincide with a vertical plane passing through the cylinder central axis in parallel with T. This vertical plane is the cross section of FIG. 2, and FIG. 2 shows a central cross section of the fuel spray F in the width direction. Of course, the fuel injection valve 1 may have a circular injection hole and inject fuel in a columnar or conical shape.

By the way, the strength of the tumble flow T formed in the cylinder in the intake stroke changes in accordance with the kinetic energy of the intake air flowing into the cylinder which changes in accordance with the engine operating state. The kinetic energy of intake air is expressed by 1/2 · mv ² , m is the intake air mass per unit time, and v is the intake air flow velocity. The kinetic energy increases as the engine speed increases or the engine load increases as the engine operating state. That is, it is large at high rotation and high load and small at low rotation and low load. Further, the kinetic energy of the intake air flowing into the cylinder becomes larger as the combustion air-fuel ratio is on the lean side in the engine operating state. When the combustion air-fuel ratio is switched from one of the set lean air-fuel ratio, the stoichiometric air-fuel ratio, and the set rich air-fuel ratio to the other, the order of the set lean air-fuel ratio, the stoichiometric air-fuel ratio, and the set rich air-fuel ratio. Thus, the kinetic energy of the intake air flowing into the cylinder becomes small. The strength of the tumble flow T increases as the kinetic energy of the intake air flowing into the cylinder increases. Thereby, if the injection rate of the fuel spray F injected from the fuel injection valve 1 is made relatively low and constant, the tumble flow T cannot be strengthened when the relatively strong tumble flow T is formed. Further, when the injection rate is relatively high and constant, when a relatively weak tumble flow T is formed, the fuel spray F may penetrate the tumble flow T and collide with and adhere to the cylinder bore, thereby diluting the engine oil. .

  In order to solve this problem, in this embodiment, fuel injection is performed using a fuel injection valve 1 in which the lift amount of the valve body is variable in at least two stages, a high lift amount and a low lift amount. When the kinetic energy of the intake air supplied into the cylinder is equal to or higher than the set value, the valve element is opened with the high lift amount L1, as indicated by the solid line in FIG. At this time, a relatively strong tumble flow is formed in the cylinder. However, since the injection rate is increased by opening the valve body with the high lift amount L1, the penetration force of the fuel spray F is increased, so that the fuel spray is increased. F can sufficiently strengthen the tumble flow T.

  On the other hand, when the kinetic energy of the intake air supplied into the cylinder is smaller than the set value, the valve element is opened with a low lift amount L2, as indicated by a dotted line in FIG. At this time, a relatively weak tumble flow is formed in the cylinder, but the injection rate is lowered by opening the valve with the low lift amount L2, and the penetration force of the fuel spray F is weakened. It is possible to suppress sticking through the flow and colliding with the cylinder bore. In addition, the relatively weak tumble flow can be surely strengthened by the fuel spray F having a low penetration force.

  In the present embodiment, the fuel injection end timing is fixed at the intake bottom dead center (BDC), so that the valve is opened in consideration of the injection rate so that the required fuel amount is injected in each engine operating state. The time (t1 or t2) is calculated, and the fuel injection start timing is set so that the calculated valve opening time is realized. As a matter of course, when the injection rate is high, the valve opening time for injecting the same amount of fuel is shorter than when the injection rate is low.

  If the injection rate is lowered and the injection time (valve opening time) is made longer, the injected fuel is more easily dispersed throughout the cylinder using the tumble flow, and a good homogeneous mixture is formed in the cylinder. It is advantageous. Thereby, it is preferable to change the injection rate in more stages so that the injection rate becomes lower as the strength of the tumble flow is weaker. In order to realize this, the lift amount of the valve body may be controlled in more stages using a piezoelectric actuator or the like.

  When the valve body can be controlled only in two stages of the high lift amount L1 and the low lift amount L2, as shown in FIG. 4, the valve body is continuously opened with the high lift amount L1 and the low lift amount L2. By making the valve, the overall injection rate of this fuel injection is the maximum injection rate when the valve body is opened only by the high lift amount L1, and when the valve body is opened only by the low lift amount L2. The injection rate can be between the minimum injection rate and the minimum injection rate. Of course, the continuous opening of the valve body with the high lift amount L1 and the low lift amount L2 is performed with the low lift amount L2 even if the valve opening with the high lift amount L1 is performed before the valve opening with the low lift amount L2. The valve opening may be before the valve opening with the high lift amount L1.

  FIG. 4 shows a case in which half of the required fuel amount corresponding to the current engine operating state is injected with the high lift amount L1, and the other half is injected with the low lift amount L2. The rate is an intermediate injection rate between the maximum injection rate and the minimum injection rate. As a matter of course, the valve opening time t1 ′ of the high lift amount L1 for injecting half of the required fuel amount is shorter than the valve opening time t2 ′ of the low lift amount L2 for injecting the remaining half of the required fuel amount. Become. The fuel injection start timing is set so that the intake bottom dead center is obtained when these two valve opening times t1 'and t2' are continuously realized.

  When the injection rate is increased from the intermediate injection rate between the maximum injection rate and the minimum injection rate, the amount of fuel injected with the high lift amount is made more than half of the required fuel amount, and the amount of low lift is reduced accordingly. The amount of fuel injected may be less than half of the required fuel amount. In addition, when the injection rate is set lower than the intermediate injection rate between the maximum injection rate and the minimum injection rate, the amount of fuel injected with a high lift amount is set to be less than half of the required fuel amount, and the amount is reduced accordingly. The amount of fuel injected by the lift amount may be set to be larger than half of the required fuel amount.

  Thus, the larger the ratio of the fuel amount injected with the high lift amount out of the required fuel amount (the proportion of the fuel amount injected with the low lift amount becomes smaller accordingly), the injection rate becomes smaller. The injection rate can be lowered as the ratio of the fuel amount injected with a high lift amount decreases (the proportion of the fuel amount injected with a low lift amount increases accordingly) Can do. As a result, the lower the strength of the tumble flow formed in the cylinder, the lower the injection rate, the fuel injection becomes possible, and the fuel spray F can be surely strengthened so as not to penetrate the tumble flow. At the same time, since the penetration force of the fuel spray is not increased unnecessarily, the dispersion of the injected fuel using the tumble flow is promoted, which is advantageous for forming a good homogeneous mixture.

  In the present embodiment, the fuel injection end timing is the intake bottom dead center, but this is not a limitation of the present invention, and it is sufficient that the fuel injection is performed mainly at the end of the intake stroke. The timing may be near the intake bottom dead center.

It is a bottom view of a cylinder head showing an embodiment of a cylinder injection type spark ignition internal combustion engine by the present invention. It is a schematic longitudinal cross-sectional view of the cylinder injection type spark ignition internal combustion engine of FIG. It is a time chart which shows the lift pattern of a valve body. It is a time chart which shows another lift pattern of a valve body.

Explanation of symbols

1 Fuel Injection Valve 2 Spark Plug 3 Piston T Tumble Flow F Injection Fuel

Claims (3)

  A cylinder having a fuel injection valve disposed substantially at the center of the cylinder upper portion and a spark plug disposed at the upper portion of the cylinder, and descending along the exhaust valve side of the cylinder bore and rising along the intake valve side of the cylinder bore In order to intensify the tumble flow turning inside, the fuel is injected by the fuel injection valve toward the exhaust valve side of the cylinder bore at the end of the intake stroke, and the kinetic energy when the intake air that generates the tumble flow flows into the cylinder An in-cylinder spark-ignition internal combustion engine characterized by lowering the injection rate of the fuel injected from the fuel injection valve when the kinetic energy is small compared to when the kinetic energy is large.   2. The direct injection spark ignition internal combustion engine according to claim 1, wherein the injection rate of the fuel injected from the fuel injection valve is lowered as the kinetic energy of the intake air generating the tumble flow is smaller. .   The fuel injection valve can control the valve body in two stages of a high lift amount and a low lift amount, and fuel injection at a maximum injection rate is realized by opening the valve body by the high lift amount, and the low injection amount is achieved. The fuel injection with the minimum injection rate is realized by opening the valve body with the lift amount only, and the injection rate between the maximum injection rate and the minimum injection rate is that the valve body has the high lift amount and the low lift rate. 3. The direct injection spark ignition internal combustion engine according to claim 2, which is realized by continuously opening the valve at one and the other of the quantities.

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